Expansion of Air on Heating

Hot Air Balloons use simple physics to give a tranquil sense of flight.

The 'envelope’ of the balloon is made of a strong yet light nylon fabric with a burner attached to it.

The pilot fires the burner and aims the flame into the mouth of the balloon to heat the air inside it.

The balloon gradually gets inflated and rises up in the air.

A simple application of Physics concepts allows the balloon to inflate and take flight.

That is, air when heated expands.

Also, the density of hot air is less than the density of cold air.

As we heat the air inside a balloon, the air inside it expands, inflating the balloon.

Also, the density of the air inside the balloon becomes less than the relatively colder air in its surroundings.

As a result, the balloon gradually rises up in the air.

Let us perform an experiment to see how air expands on heating.

In order, to perform this experiment we require a glass bottle, a balloon, a tub of warm water and a tub of cold water or ice.

We begin by tightly tying a balloon at the neck of a glass bottle.

Next, we place the bottle along with the balloon tied to it in a bucket of warm water.

As soon as we place the bottle in the bucket of warm water, the balloon is found to inflate a little on its own.

Next, we place the bottle along with the balloon tied to it in a bucket of ice cold water.

As we place it in the bucket of ice-water, we find the balloon deflated.

Hence, we can now safely conclude that air expands upon heating and likewise compresses when the temperature is reduced.

Let us now see why this happens.

When we place the bottle in a bucket of hot water, the temperature of the air inside it increases.

When the temperature of air increases, the kinetic energy of the air molecules increases too.

This increase in kinetic energy results in the air molecules moving faster than before as a result of which they occupy more space.

The molecules occupying more space than before subsequently results in air expanding.

Like we saw in the case of a hot air balloon, as the air was heated it expanded and inflated the balloon.

Similarly, when we placed the bottle in a tub of ice-water, the temperature of the air in it decreased.

Consequently, the air molecules also lost kinetic energy as a result of which they began to move slower than before.

As the molecules moved slower than before, they occupied less space and the air compressed.

Revision

When air is heated, the kinetic energy of the molecules increases as a result of which they begin to move faster than before

As the air molecules move faster than before, they begin to occupy more space and the air expands

Vice versa, when air loses temperature, it compresses.

The End